from the PCB design I would like to highlight some things and ask some questions.

Should the amplifier not rather be modular, in other words I design it so that there are ribbon connectors plug-in from one board to another, thus make each a separate board for example, tone control, amp, crossfeed, psu, etc.

What is the down side. PCB manufacturers charge a set-up cost for every type of board, making a single board with everything on results in a single set-up cost which is a standard cost.

However, the cost of the board is related to real estate and number number of through hole plates. Thus the bigger the board the more expensive.

Smaller boards are cheaper (and the chances of being single sided is better and even cheaper still) but since some people may select not to buy the tone control board or whatever would drive each small board cost up slightly as fewer divide into set-up costs.

How would you guys want me to handle the PCB design.

I don't believe this project can bear the complexity of multiple boards - I'm prepared to stock and pass on boards in North America (EU too if nobody there to pick up the honour) and therefore minimize shipping costs for everyone - but I don't want to have to sort out multiple options

For small runs, the set up charges usually dominate the costs. You have more files to generate and check. More boards to mount onto the chasis. Connectors are potential points of failure.

One board is my preference.

__________________"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.

__________________"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.

I agree with Gareth. It should be one board, double sided only if necessary, all options on the one board. I have decided to go single rail, with regulator, no chokes to save space and weight, and virtual earth to scotch hum, which is a major concern in this project.

Tone controls with IC buffer, defeat switch, DC coupled tone control to amp, switchable crossfeed and output series resistor. Target is 12Vpp output, around 9mW into 2K phones, and much more into 24R. Amp remains as discussed, diode biased, Class A at low levels, shifting to AB at higher levels. This will be a very good headphone amp, one of the best around, should take some beating.

We are very fortunate having the expertise of Nico and Gareth, and I thank them for their valued input.

Thank you all for chiming in to offer support. Collaborative design must be properly communicated to all players, and I appreciate your interest.

Gareth, I grew up on a farm. All I ever ate was mutton, I grew tired of it. I married a Javanese lady and now I eat mostly Asian food, which is very healthy and wards off heart disease..... in the west we all eat too much red meat.

As you know, I married a lady from somewhere very close to Java and also enjoy the delights of Asian cooking. But an English boy never forgets his mum's cooking....

__________________"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.

"Originally Posted by Nico Ras
One final question. This is regarding the headphone impedance, I know of some having a low impedance around 32 ohms, most decent headphones have a much higher impedance around 200 - 500 ohms, why did we select 23 Ohms and why a 1000 uF pass capacitor, anyone though about that? As it stands the frequency is 7Hz, anybody listen to this?"

My headphones are AudioTechnica ATH-AD700. Not exactly top shelf, but about as good as I can afford and I'm pretty happy with them. They are 32 ohms and I'm sure there are others out there with something similar.

Thanks to everyone for your great efforts.

I think I can answer this, the new design is calling for a 10 ohm output resistor and a 120 ohm resistor switchable for different impedance headphones. The 120 ohm should work well for the lower impedance headphones like your ATH-AD700 and the 10 ohm resistor mates up for higher impedance HP's like the Sennheisers or anything with an impedance greater than 250 ohms.

Not wishing to belabor a point or offend our NZ mates, but the sheep 'entry' reminds me of the following joke which only makes sense if you can pick the difference between Aussie and Kiwi accents.......

An Australian is driving through New Zealand on holiday when he comes
across a local 'enjoying' a sheep in a paddock.

The Aussie yells "Hey mate, we shears our sheep in Australia!"

The Kiwi replies "No worries mate, but in New Zealand we don't share our sheep with anybody"